To understand why 2nd and 4th angle projection is not used? First we need to understand the concept behind orthographic projection system.
Theoretically there are four projection system, out of which only 1st and 3rd angle projection system are used because of limitation of 2nd and 4th angle projection system. In this article we will understand those limitations.
How Projection System Works?
To understand how projection system works We can consider a point in 1st and 3rd quadrant (refer image on right)
Consider Point A in 1st quadrant that lies in between observer and projection plane. Front view of point A will be in vertical plane (V.P.) and top view will be on horizontal plane. To draw front and top view in 2D plane, according to rule of projection, horizontal plane (HP) need to be rotated by 90 degree in clockwise direction.
Now the obvious question that comes to our mind : Why 2nd angle and 4th angle projection is not used ?
Now let’s consider object is placed in 2nd or 4th quadrant.
To draw view in 2D plane, when horizontal plane (HP) is rotated by 90 degree in clockwise direction front view and top view will overlap, which is not advisable.
We can conclude here because of overlapping of front and top view 2nd and 4th angle projection system is not used.